Re: [RFC PATCH -next 13/16] mm/damon/sysfs: ensure valid addr_unit setting in damon_sysfs_apply_inputs()

[Quanmin Yan]

Hi SJ,

在 2025/8/14 1:02, SeongJae Park 写道:
> On Wed, 13 Aug 2025 13:07:03 +0800 Quanmin Yan <yanquanmin1@xxxxxxxxxx> wrote:
>
> > By calling damon_sysfs_turn_damon_on(), the execution of damon_commit_ctx()
> > can be bypassed. Therefore, it is necessary to prevent ctx->addr_unit from
> > being set to 0 in damon_sysfs_apply_inputs() and update min_region to avoid
> > potential issues.
> Nice catch!
>
> > Signed-off-by: Quanmin Yan <yanquanmin1@xxxxxxxxxx>
> > ---
> >   mm/damon/sysfs.c | 3 ++-
> >   1 file changed, 2 insertions(+), 1 deletion(-)
> >
> > diff --git a/mm/damon/sysfs.c b/mm/damon/sysfs.c
> > index bea782b0a711..122824776c1d 100644
> > --- a/mm/damon/sysfs.c
> > +++ b/mm/damon/sysfs.c
> > @@ -1422,7 +1422,8 @@ static int damon_sysfs_apply_inputs(struct damon_ctx *ctx,
> >   	err = damon_select_ops(ctx, sys_ctx->ops_id);
> >   	if (err)
> >   		return err;
> > -	ctx->addr_unit = sys_ctx->addr_unit;
> > +	ctx->addr_unit = sys_ctx->addr_unit ? : 1;
> So this is fixing a bug of the seventh patch ("mm/damon/sysfs: implement
> addr_unit file under context dir") of this series, right?  It is better to not
> add a broken patch, and then fixing it in the same series.  Let's squash the
> fix of the problem into the patch.  Don't forget adding your Signed-off-by on
> the patch.
>
> Also, since sys_ctx->addr_unit is initialized as 1, the value being zero is
> user's wrong input.  Let's return -EINVAL instead of making it silently
> success.

Thank you for the kind reminder! The relevant changes have been integrated into
patch #7 of the v2 series[1]. It's worth noting that we've already prevented users
from inputting 0 at the source, therefore "ctx->addr_unit = sys_ctx->addr_unit;"
has been retained in the v2 version.

[1] https://lore.kernel.org/all/20250820080623.3799131-8-yanquanmin1@xxxxxxxxxx/

> > +	ctx->min_region = max(DAMON_MIN_REGION / ctx->addr_unit, 1);
> Seems this is a fix of an issue in the 12th patch ("mm/damon: add
> damon_ctx->min_region and damon_target->min_region") of this series?  Let's fix
> it on the patch.

This set of changes has been integrated into patch #11 of the v2 series[2].

[2] https://lore.kernel.org/all/20250820080623.3799131-12-yanquanmin1@xxxxxxxxxx/

Thanks,
Quanmin Yan